Musnad Ahmad 3:44

Abu Sa’id, the freed slave of Banu Hashim, narrated to us, Ibn Lahi’ah narrated to us, Zuhrah ibn Ma’bad narrated to us, from Abu Salih, the freed slave of ‘Uthman, that he narrated to him, saying: I heard ‘Uthman saying in Mina: "O people, I am narrating to you a hadith I heard from the Messenger of Allah, peace and blessings of Allah be upon him, saying: 'A day of guarding in the way of Allah is better than a thousand days in other than it, so let a man guard however he wishes.'" Have I conveyed [the message]? They said: "Yes." He said: "O Allah, bear witness."